This underwater sinkhole attracts divers far and wide as the holy grail of dive sites. What was once a limestone cave in the past soon collapsed into a sinkhole that’s 1,000 feet wide and over 400 feet deep. Back in 1971, renowned underwater explorer Jacques Cousteau deemed the mysterious Great Blue Hole as one of the top ten dive sites in the world as he sailed down the hole in his ship Calypso and explored its secrets in his TV show The Undersea World of Jacques-Yves Cousteau.